"We demand the immediate declassification of this CBI file to set the historical facts right. The people
of India would like to know who passed on information to British intelligence for which Sarat Chandra Bose, Subhas Bose's elder brother, went to jail," the family said in a press release in Kolkata.

Chaudhuri, best known for 'The Autobiography of an Unknown Indian', was the secretary of Sarat Chandra Bose in 1938.

In 1941, a day before Sarat was arrested by the Britishers, Chaudhuri had quit the job and joined the All India Radio.

Later he shifted to England and was honoured with the title of Commander of Order of the British Empire.

Netaji's grandnephew and family spokesperson Chandra Kumar Bose said "it is clear that he was in secret connivance with the Britishers and leaked information about the whereabouts of Sarat, leading to his arrest."

The family said that after Independence, CBI had investigated the role of Chaudhuri but kept the report secret.

The statement issued by the family said that in late 1967, Sarat's son Amiya Nath Bose had asked Indira Gandhi to show him the CBI file on Chaudhuri. But the then CBI chief DP Kohli refused.

"On being asked by Indira Gandhi as to why he did not bring the file, Mr Kohli said in the presence of our father (Amiya), "No, madam, I cannot give this file. The contents are extremely volatile and if the information is made public, Nirad C Chaudhuri's life would be in danger," said the statement.

Chandra Bose said Netaji had never liked Nirad C Chaudhuri and used to tell Sarat Bose to sack him.

"By not doing so was the most grievous mistake Sarat Bose made, which ultimately sent him to prison," he said.